Complementary metal oxide semiconductor (CMOS) process scaling over the past decade has produced smaller devices through the integration of increasing numbers of transistors. For example, current microprocessors are more than a thousand times more powerful than microprocessors made a decade ago.
Power dissipation of microprocessors has also increased. Some microprocessors now dissipate more than 100 W. Modem processors built using low voltage CMOS processes employ a supply voltage level that barely exceeds 1 V. As a result, CMOS-based microprocessors require current levels that exceed 100 A.
Physical barriers are beginning to limit the amount of current flowing through these devices. One barrier relates to the voltage drop associated with the distribution of power to these microprocessors. A parasitic resistance of 1 mΩ milliohm in chip packaging and/or printed circuit board (PCB) power planes can create 100 mV of voltage drop. In reality, it is extremely difficult to lower the parasitic resistance to less than 1 MΩ megaohm without significantly increasing material and associated processing costs.
For example, the resistance of a gold bond wire in typical semiconductor packaging has a resistance of about 100 MΩ for a 1 micron diameter and 5 mm length. To limit the total power supply resistance to less than 1 MΩ, each power supply connection (VDD and VSS) must be limited to less than 0.5 MΩ. This approach requires more than 400 bond wires. A lot more bond wires will be required due to other sources of parasitic resistance.
One approach eliminates the bond wires and uses flip chip packaging technology. This approach solves half of the packaging resistance problem. Additional considerations include the resistance of the metal within the semiconductor itself, the metal resistance of the flip chip packaging, and the metal resistance of the printed circuit board (PCB) must also be accommodated. As the chips continue to shrink, the traces of the wiring must be made narrower. As a result, thinner metal material must be used, which in turn increases the parasitic resistances.